The "blade" is about 4 ft long, but it feels a bit more fragile than some of the shark tooth clubs i've handled.

yeah, it's the snout off of a sawfish. My great great aunt Lucy was a Baptist missionary to China and India at the beginning of the 20th Century, and sent back an "unaltered" snout, so no grip to it. I've still got it, a century later.

They had a display of Polynesian weapons at the SD Museum of Man, including a lot of those shark tooth nasties. I wonder, though, how easily those teeth would start popping out of their mounts when subjected to the stress of combat.

I wonder if the curvature of the swords there was meant to be utilized curving back (like a katana) or forward (like a kukhri). Reminds me of an atassa, a saber-like war club favored by a number of North American indigenous:
meant to be used in either grip alignment.

I wonder, though, how easily those teeth would start popping out of their mounts when subjected to the stress of combat.

The teeth are set in a fairly snug groove on the sturdier ones, and were of course meant to be used on nearly bare flesh.
I think you're right for the most part though, especially with holes drilled in the teeth.

I like the knuckle duster version, that would suck to get punched with.